This article is from the MachTen & CodeBuilder FAQ, by Jaime Julca firstname.lastname@example.org with numerous contributions by others.
You must have physical access to the computer. During system startup, wait
until you see the "Cleaning up..." on the startup screen, then quickly press
CTRL-C two or three times. This will halt the system startup, press RETURN
one time to enter MachTen in single-user mode. You should be at a '#'
prompt. Type '/usr/bin/passwd' then change the root password when prompted.
Now run 'sync' twice from the '#' prompt, then run '/sbin/reboot'. Once
MachTen quits completely, drag and drop the MachTen_FFS or CodeBuilder_FFS
onto 'Fast File First Aid" repeatedly until FFFA gives the FFS file a clean
bill of health. Restart MachTen and login with your new root password.
G7.s. How do I create an A/UX partition for a fast file system?
As far as we know, you cannot do this with Drive Setup. We recommend using
FWB's Hard Disk Toolkit, simply set the Partition Type to Apple_UNIX_SVR2
when creating a scratch partition.
G7.t. Adduser does strange things to my Power MachTen 4.1 installation, how
can I fix it?
Please read MachTen 4.1 Adduser Problems, with Fixes.